Electrical discharge device



Jan. 16, 1934. c. SPAETH ELECTRICAL DISCHARGE DEVICE Filed Aug. 20. 1929 INVENTOR.

cl-maues 5 Pa erFH ATTORNEY Patented Jan. 16, 1934 UNITED STATES PATENT OFFICE 8 Claims.

This invention relates to electrical discharge devices, and more particularly to gas-filled devices adapted for illuminating purposes.

An object of this invention is the provision of a high intensity diffused light source the color of which may be adjusted'at will in a predetermined manner.

Another object of this invention is to produce a gaseous discharge illuminating device capable 10 of producing white light approximating that of the sun.

A further object of this invention is to provide an electrical discharge tube having "a gas filling, and means whereby the color emitted from the tube may be varied in any desired manner.

Another object is the provision of an illuminating device which is adapted to produce light high in actinic value and adapted for ordinary photographic purposes, and for photography in colors.

Still another object is the construction of an electrode chamber which is adapted to retain metallic electrode material of low melting point, without permitting escape of the metal, when in a molten or plastic condition, into the discharge path of the device.

In accordance with my invention, I construct a tube comprising an evacuated envelope having a filling of conducting gas, a main discharge circuit and an auxiliary discharge circuit. The main circuit serves to pass a discharge through the gas column, while the auxiliary circuitserves to pass a discharge to a quantity of mercury or other suitable material to form a vapor which enters the main discharge path and causes a modification of the light emitting characteristics thereof.

White light may be produced by filling the tube with neon gas, either in a pure state or containing a small percentage of helium, and utilizing mercury in the auxiliary electrode circuit. By properly proportioning the value of the auxiliary circuit current to that of the main cir-.- cuit current the rays emitted by the mercury vapor may be made substantially complementary to those of the neon gas whereby the luminous effect will be white. By decreasing the auxiliary current the emitted light may be made more red while by increasing said current the light 0 may be made more blue. The addition of but a small amount of mercury vapor to the gas column, even so small as to have but slight effect on the color of the emitted light, greatly increases the current density of the discharge, and consequently the luminous effect. On the other hand by operating the device with a large amount of mercury vapor discharges of very high current densities are obtainable. The character of the light given oil, while then approximately that or a mercury arc, will be softened and made less harsh.

An extremely important feature of the invention from the photographic view point, is its versatility. Merely by varying the current passing to the auxiliary electrode it is possible to vary the color of the light generated to suit any scene. Elaborate and expensive make-up is not needed for the actors, as by adjusting the currents of the lamp circuits to the proper values the desired hue may be secured. Furthermore the luminous effects may readily be so selected as to suit any type 01' film. If red ought to be more prominent it is only necessary to decrease the auxiliary circuit current so as to lessen the intensity of the blue component.

Good results may be obtained with various rare gas mixtures; for example, neon and helium,

where the percentage of helium is relatively large, e. g., 45. This mixture may be made to produce white light by adding the proper amount of mercury vapor from the auxiliary electrode. The addition of helium strengthens the emitted light in the green portion of the spectrum.

The spectrum of the emitted light may be varied by using other mixtures of rare gases if desirable.

It is preferable, where the device is to be used on low potential circuits, to make one of the main electrodes of an alkali metal or alloy so as to reduce the contact potential thereof. In order to prevent any of the alkali metal from running out into the light radiating portion of the tube when in a molten or plastic condition, I arrange a screen of fine wire mesh or gauze. This screen which may be of nickel, for example, is so fine as to act as a complete barrier for molten metal, while at the same timepermitting the passage of the electrical discharge. Where the auxiliary electrode is of mercury, a similar gauze screen or partition is used to retain the mercury in its proper position. I

The above mentioned and further objects and advantages and the manner of attaining them will be made clear in the following description and accompanying drawing.

In the drawing, Fig. 1 illustrates an electrical discharge device constructed in accordance with my invention; and

Fig. 2 shows a modified form of electrical discharge device embodying my invention, which is adapted to operate on alternating current.

Fig. 3 illustrates an arrangement of discharge tubes and ballast lamps which may be used.

Referring more particularly to the drawing, reference numeral 1 indicates an envelope of glass, such as Pyrex or other suitable material, having at one end an electrode 2, and at the other end an electrode structure 3. The electrode structure 3 comprises a quantity of alkali metal 4 which may be, for example, 90% potassium and 10% caesium, and a conducting body of material 5. A lead-in wire 6, preferably of tungsten, is secured to the body 5 and is sealed through the wall of the tube at '7. It will be noticed that the wall of the envelope is bent inwardly to form a reentrant portion at 7. This is in order to maintain the seal of the lead-in wire in close contact with the alkali metal, whereby cracking of the seal, due to unequal cooling of the diflerent portions of the envelope adjacent the seal, will be prevented. By having the sealed portion turned inwardly, the temperature thereof is caused to vary substantially in step with that of the rest of the envelope, so that the seal cools no more quickly than the rest of the envelope. Where the seal is turned outwardly in accordance with the usual procedure, the projecting portion drops in temperature quickly, while the rest of the envelope adjacent thereto is kept hot by the heatgiven oil from the molten alkali metal. This difierence in temperature between the two parts in many cases causes fracture of the seal and the consequent destruction of the vacuum in the tube. The function of the body 5 is to insure a good contact between the lead-in wire and the alkali metal. The lead-in wire may be subjected during the construction or operation of the tube, to such conditions as to receive a coating of oxide which is non-conductive. The immediate result is that the point of contact between the alkali metal and the lead-in wire is made very small and the discharge on the small in any well-known manner.

area becomes very intense, so intense, in fact, that the alkali metal is sputtered with a good deal of force around the inside of the tube and erratic action of the entire device follows. By providing the conducting body 5, which I find may be advantageously of nickel, perfect contact between the lead-in wire and'the electrode is assured.

.Not only is the area of contact with the alkali metal larger, but the element 5 is also less subject to the formation of an oxide coating.

In order to further insure against the sputtering of molten metal into the main body portion of the tube, an internal barrier arrangement is utilized. This may comprise a tube 8 projecting inside of the electrode chamber 9. In operation, any particles of molten metal which are sputtered from the electrode will be prevented from leaving the chamber by striking the barrier 8. Likewise,

if the tube is turned upside down while the metal 4 is molten, the greater part thereof will be caught between the wall 9 and the barrier 8 and thereby prevented from running down into the tube. For preventing any particles of the molten metal which may pass within the barrier 8 from entering the tube, a perforated barrier or partition 10 is arranged across the inside of the tube adjacent the outlet of the chamber 9. This partition, I find, may with good results be constructed of nickel wire gauze of about 60 mesh. This gauze partition may be placed loosely in a groove 11 provided in the wall of the tube, but it is preferably welded directly into the walls of the tube By such welding assurance is had that the molten metal will not run down around the outer edge of the partition into the main body of the tube.

The atmosphere of the device preferably comprises a filling of neon at a pressure of approximately 3 mm. of mercury, but other rare gases at different pressures may be used to obtain different results.

In order to vary the spectrum characteristics electrode chamber or appendix 12 is provided.

This auxiliary electrode arrangement is built in substantially the same manner as 3. A chamber 13 serves to contain a quantity of mercury 14 to which connection is made by a lead-in wire 15. Barriers 16 and 17, similar in 8 and 10, are used for preventing the body of mercury from leaving chamber 13 and entering the main discharge path of the tube 1.

When the device is to be operated in a vertical position, the electrode chambers 9 and 13 may be arranged as illustrated, but it will be understood that if it should be desired to use the device horizontally, the chambers would preferably be built angularly with respect to the main body portion of the tube, so that metallic electrode fluid would remain in its proper position in the chambers.

For energizing the tube a supply circuit 18 is connected on one side to the lead-in wire 6 by means of a conductor 19, and to the electrode 2 by a lead 20 having a ballast resistance 21 in series therewith. The auxiliary electrode 12 is connected to the line conductor 20, through a lead 22 having a variable resistance 23 in series therewith.

Where a low potential source is used at 18, some auxiliary starting device may be necessary. One suitable mechanism for this purpose is a highirequency high-voltage generator 24 having its input circuit connected across the line 18 with a control switch 25 in series therewith. The output terminal of the generator may be connected to a clip 26 placed around or adjacent to the envelope 1 intermediate the ends thereof and to a similar clip near the appendix 12.

I find that with a tube of 120 cm. length and 3 cm. diameter, provided with metallic electrodes as shown, white light may be obtained from the device when connected to a source 18 of 220 v. by utilizing at 21 a resistance consisting of five 110 v. 100 w. tungsten lamps in parallel, and adlusting the resistance 23 to 140 ohms. In general, it may be said that white light may be produced by passing through the main circuit a current approximately ten times as great as that passed through the auxiliary circuit.

With any specific device constructed in accordance with this invention it is possible, by observing the intensities of the main and auxiliary currents which produce a certain color effect. to reproduce that effect at any time in the future merely by adjusting the currents to the observed values.

During operation, the lamp bank 21 serves both as a positive resistance to overcome the negative resistance characteristic of the tube 1, and to produce illumination supplementing that of said tube.

If the device is to be operated from a relatively high potential source the electrode structure 3 may be replaced by an ordinary electrode such as 2.

In Fig. 2 a full wave alternating current tube is illustrated. This tube comprises an envelope 1 having at one end an electrode structure 3 similar to that shown in Fig. 1, and at the other end a pair of electrodes 27 and 28 which. are placed relatively close together. An auxiliary electrode similar to 12 is provided. The electrode structure may be placed vertically, as shown, in which case the mercury will assume the position illustrated in the drawing. Current is supplied to the device by a transformer 29 of the high leakage type having a center tapped sec-= ondary. This transformer may either be of the type having a specially constructed core so that current therefrom is maintained substantially constant, or may be of the ordinary constant potential type with a reactance coil in series with the primary thereof. With this type of transformer no ballast resistance 21 is necessary. The two end terminals of the transformer secondary are connected to the electrodes 27 and 28, and the intermediate tap is connected to the electrode 3. The auxiliary electrode circuit may be energized by connecting the electrode 12 through its resistance 23 to either electrode 27 or 28.

Where the device is used on direct current the auxiliary electrode is preferably connected to the positive side of the line, as shown in Fig. 1.

White light may. be obtained by using a neon gas filling of approximately 3 mm., and by pro viding currents in the main and auxiliary circuits of substantially a 10 to 1 ratio, as that mentioned in connection with Fig. 1. Where the potential impressed across the electrodes 2'7 and 28 (Fig. 2) is 440 v., I find that the spacing thereof may sat- A isfactorily be 5 mm., while the distance between the electrodes 27, 28 and. 3 may be 120cm. With this arrangement no appreciable discharge passes between the electrodes 27 and 28, but a heavy discharge takes place between each of these electrodes and the electrode 3.

Lamps may be used as a ballast resistance at 21, or a plain resistance may be used as desired. Where lamps are used the light produced thereby serves to supplement that of the discharge tubes. As ordinary tungsten lamps emit a large proportion of red light it may be found necessary or desirable proportionately to increase the blueness of the discharge tubes.

The arrangement shown in Fig. 3 is particularly useful in combining the rays emitted by the two kinds of devices. With this arrangement the difiused light given off is a combination of the continuous spectrum of the incandescent lamps 31, which may be used as ballast resistance, and the neon-mercury spectrum of the discharged tubes 32. Because of the large amount of red light emitted by the incandescent lamps the discharge tubes may be run with a comparatively large proportion of mercury vapor, so that they are blue in appearance to the eye. Where heat has to be considered it is preferable to place the ballast resistance in some remote spot and rely entirely on the discharge tubes for illumination, the emitted rays being enriched with red, by proper adjustment of the auxiliary circuit.

I have described a specific form of device embodying my invention for the purposes of illustration but wish it to be understood that the invention is capable of a. variety of modifications and adaptions, which will readily occur to one skilled in the art, and which may be made without departing from the spirit of the invention as expressed in the following claims.

What I claim is:

1. In an electric discharge device, an electrode structure comprising a chamber having an outlet opening therein, .a tube projecting within said opening and sealed to the chamber at the edge thereof, a quantity of alkali metal in said chamber, a lead-in wire of tungsten sealed through the walls of the envelope, and a piece of nickel welded to the end of the wire and supported by said tungsten wire in such position to be in contact with the alkali metal bath when the alkali metal becomes liouid by heatin 2. In an electrical discharge device according with claim 1, a seal for the lead-in wire of a low melting point electrode, wherein the envelope at the point of juncture with the lead-in wire is turned inwardly and the electrode material is positioned in direct contact with said envelope at said point of juncture.

3. An electrical discharge device adapted to produce and maintain a light having a color value intermediate the spectrum of neon and mercury, comprising a transparent envelope containing an atmosphere comprising neon at approximately 3 mm. pressure, said envelope being approximately 120 cm. long and 3 cm. in diameter, an electrode of alkali metal at one end of the envelope, a main electrode and an auxiliary mercury electrode at the other end of said envelope, resistances of approximately 25 ohms and 140 ohms in series with said main and auxiliary electrodes, respectively, and a source of 220 volts for causing currents ,to pass between the electrodes at one end of said envelope and the electrode at the other end'of said device.

4. In an electrical discharge device adapted to produce and maintain a light having a color value intermediate the spectrum of neon and mercury, an elongated envelope having a rare gas as filling, a pair of electrodes positioned in one end of said envelope, an alkali metal electrode at the other end of said envelope, an auxiliary mercury electrode, a transformer having a high leakage characteristic, connections from the secondary to said pair of electrodes, a connection from an intermediate point of said secondary to said alkali metal electrode, and a connection including a variable resistance between one of said pair of electrodes and said mercury electrode.

5. An arrangement in accordance with claim 4 wherein the length of the envelope is 120 cm.,

the diameter 3 cm., the spacing of the pair of electrodes is .5 cm., and the voltage impressed between said pair of electrodes is 220.

'6. In an electrical discharge device, an open ended envelope containing a rare gas, a chamber having connection with the said envelope beyond its open end, the open end of said envelope extending into said chamber, a metallic electrode of low melting point positioned in the chamber, said metallic electrode being adapted to become liquid when heated, a fine wire mesh gauze positioned in the gas envelope and inside of the open end thereof to prevent the escape of the liquid electrode material from the chamber.

7. A device in accordance with claim 6 wherein the envelope is of .borosilicate glass, the electrode of alkali metal and the gauze nickel.

8. In a light emitting tube, an envelope, a rare gas in theenvelope, electrodes near the opposite ends of the envelope, the rare gas normally resisting the passage of current between saidelec-- trodes, a mercury chamber having connection with said envelope, means to vaporize the mercury in predetermined quantities suflicient to modify the spectrum of the rare gas'to produce a predetermined color value, a starting device, comprising a high frequency, high voltage generator, having connection with the said envelope at spaced portions thereof, the high frequency generator when energized ionizing the rare gas 145 in the envelope and causing current to flow between said electrodes through the ionized gas and means to control the operation of said generator.

CHARLES SPAETH. 

